What do you do if one of your friends always tells things to your other friends that you do not want your other friends to know?

This friend that you speak of, doesn't sound very trust worthy.

You could talk to your friend, tell them that you don't appreciate them telling your other friends your personal things. That when you talk to your friend you're confiding in them and trusted that they wouldn't tell other people what your thoughts. Something to that extent.

Or you could not trust that your friend will keep your thoughts to themselves and stop telling them your personal problems.

These are mere suggestions, but I hope that my advice helps you out.

If you'd like to talk you can message me if you'd like.